Association of Neighborhood-Level Household Income With 21-Gene Recurrence Score and Survival Among Patients With Estrogen Receptor–Positive Breast Cancer

IMPORTANCE: While low income has been associated with a higher incidence of triple-negative breast cancer, its association with 21-gene recurrence score (RS) among patients with estrogen receptor (ER)-positive breast cancer remains unclear. OBJECTIVE: To evaluate the association of household income with RS and overall survival (OS) among patients with ER-positive breast cancer. DESIGN, SETTING, AND PARTICIPANTS: This cohort study used data from the National Cancer Database. Eligible participants included women diagnosed between 2010 and 2018 with ER-positive, pT1-3N0-1aM0 breast cancer who received surgery followed by adjuvant endocrine therapy with or without chemotherapy. Data analysis was performed from July 2022 to September 2022. EXPOSURES: Low vs high neighborhood-level household income levels defined as below vs above the median household income of $50 353 based on each patient’s zip code. MAIN OUTCOMES AND MEASURES: RS (a score ranged from 0 to 100 based on gene expression signatures indicating the risk of distant metastasis, with RS of 25 or below indicating non–high risk and RS above 25 indicating high risk) and OS. RESULTS: Among 119 478 women (median [IQR] age, 60 [52-67] years; 4737 [4.0%] Asian and Pacific Islander, 9226 [7.7%] Black, 7245 [6.1%] Hispanic, 98 270 [82.2%] non-Hispanic White), 82 198 (68.8%) and 37 280 (31.2%) patients had high and low income, respectively. Logistic multivariable analysis (MVA) showed that, compared with high income, low income was associated with higher RS (adjusted odds ratio [aOR], 1.11; 95% CI, 1.06-1.16). Cox MVA showed that low income was also associated with worse OS (adjusted hazards ratio [aHR], 1.18; 95% CI, 1.11-1.25). Interaction term analysis showed a statistically significant interaction between income levels and RS (interaction P < .001). On subgroup analysis, significant findings were noted among those with RS below 26 (aHR, 1.21; 95% CI, 1.13-1.29), while there was no significant OS difference between income levels among others with RS of 26 or higher (aHR, 1.08; 95% CI, 0.96-1.22). CONCLUSIONS AND RELEVANCE: Our study suggested that low household income was independently associated with higher 21-gene recurrence scores and significantly worse survival outcomes among those with scores below 26, but not 26 or higher. Further studies are warranted to investigate the association between socioeconomic determinants of health and intrinsic tumor biology among patients with breast cancer.